This invention relates to a series of collector compositions, and the processes for their production, that are useful in the froth flotation recovery of copper and molybdenum from partially oxidized sulfide ores, especially those whose clay content make them too slimy for treatment with standard reagents. The products are of general utility with other sulfide ores such as lead, zinc, silver, etc.
The structures proposed to produce the new collector formulations, whose major constituent is usually a xanthogen formate, have all been known since 1927. Alkyl xanthogen alkyl formates were disclosed by Douglass, U.S. Pat. No. 1,652,099 issued Dec. 6, 1928. Dialkyl xanthic anhydrides and dialkyl dixanthates were proposed in French Pat. Nos. 634,124, 634,125, and 634,126, issued in 1927 to Guggenheim Bros. These compounds have never had practical application in mining, because the recommended reagent consumption is about ten times greater than current practice. Additionally, the flotation results did not appear to justify their use.
The compounds involved in the novel formulations are: ##STR1## Where R and R' are straight chained, branched or substituted alkyl groups with 1 to 6 carbon atoms.
The first three of these compounds are co-products of the reaction between alkyl chloroformates and alkaline alkyl xanthates involving the following reactions: ##STR2## where M is an alkali metal, and R and R' are as noted above.
Compounds (II) and (III) can be produced independently in the first case by reaction (2) above, and, in the latter by the reactions: ##STR3## where the oxidizer can be a halogen, NaOCl, H.sub.2 O.sub.2 plus acid etc.
As can be deduced from the reversibility of reaction (4), at the conditions of the reaction between a xanthate and a chloroformate, COS is given off by hydrolysis of the monothiocarbonate reducing the production of alkoxy carbonyl sulfide by reaction (3).
The effluent from reaction (6) is troublesome due to its content of alkali thiocyanate, and should be treated with acid thus: EQU MSCN+H.sub.2 O+2H.sub.2 SO.sub.4 .fwdarw.COS+MHSO.sub.4 +NH.sub.4 HSO.sub.4 ( 7)
recovering COS for reaction (4).
The dixanthogen, compound IV, can be produced by oxidation of the appropriate alkaline alkali xanthate: ##STR4##
In the manufacture of the main xanthogen formate consumed in mining, diethyl, it has been customary to minimize by-product production of diethyl xanthic anhydride, which is a yellow solid with a melting point of 55.degree. C., because at levels above 10 to 12% in the crude collector it causes freezing problems in storage at the mine, and when it comes out of solution the solid is essentially insoluble in water and thus does not contribute to sulfide mineral collection. Because of this, the original proposed use of xanthic anhydrides as collectors (French Pat. No. 234,125) indicated that it should be dissolved in an inert oil, such as kerosene.
The properties of the symmetrical dialkyl xanthic anhydrides are:
______________________________________ Mol. Density Refr Alkyl Gp Wt Phase Mlt. Pt. .degree.C. d.sub.4.sup.20 Ind. ______________________________________ Dimethyl 182.34 Solid 54-55 n.sub.D 25.degree. Diethyl 210.34 Solid 52-55 Dipropyl 238.34 Solid 55 Di-isopropyl 238.34 Solid 54-55 Dibutyl 266.54 Liquid 1.162 1.588 Di-isobutyl 266.54 Liquid 1.126 -- Diamyl 294.54 Liquid 1.107 1.568 Dihexyl 322.54 Liquid 1.078 1.541 ______________________________________
The solid xanthic anhydrides are useful as collectors, when dissolved in xanthogen formate solutions, as long as a compatible emulsifier is employed so that they do not come out of solution at normal flotation pulp temperatures (10.degree.-20.degree. C.). This metallurgical effect is shown in the flotation data of Example 7-12 below. They can also be kept in solution by the novel process of manufacturing the original ethyl xanthate, used to make the diethyl xanthogen formate, with an addition of 1 to 10% methanol to the ethyl alcohol feed.
The freezing crystallization point of different crude diethyl xanthogen formates are:
______________________________________ Composition % ______________________________________ diethyl xanthogen formate 100 70.5 62 52 diethyl xanthic anhydride -- 12.0 20 30 diethoxy carbonyl sulfide -- 8.4 8 8 inert -- 9.1 10 10 Crystallization Temp. .degree.C. -36.5 -7 +4 +14 ______________________________________
It has been found that, without a negative effect on flotation, the addition of methanol to the original alcohol used to make xanthate will significantly lower the point of crystallization. For example 6.5 molar percent of methanol added to the original ethyl alcohol and with the reaction conditions adjusted to produce a xanthogen formate which contains 30% diethyl xanthic anhydride the crystallization point is reduced from +14.degree. C. to 0.degree. C. Up to 10 molar percent methanol does not adversely affect flotation properties of the collector.